A tap tap cuts threads into the holes to accommodate screws or bolts. Taps can also be used to restore a damaged thread or to carve a new, larger one in the event of severe damage or filleting.
Steps
Step 1. Find the diameter and depth of the thread you want to make
What size should the screw be for this hole?
Step 2. Refer to Tables_for_drilling_and_lubrication a datasheet for the exact measurement of the hole diameter
For example, if you want to use an M8 x 1.25 screw tap then you will need to use a 6.6 mm drill bit. Sometimes the correct hole diameter is indicated on the same tap.
Step 3. Drill the hole of the correct diameter and length
Remember that taps generally cannot thread the full length of a blind hole all the way, so a blind hole must be a little longer than the required thread length.
Step 4. Firmly secure the piece to be threaded
Step 5. Apply a suitable lubricant such as oil, WD-40, or a specific formulation
- The WD-40 is only suitable for aluminum because it is essentially kerosene (with the CAS code of aeronautical fuel).
- Never lubricate cast iron unless you can pour a water-based coolant over it, which is only used to rinse the shavings away. Otherwise use compressed air.
Step 6. If the tap has a separate shank or tap wrench, insert it
Step 7. Hold the male aligned with the hole and rotate it clockwise
It is important to try to keep it straight as it turns. You should feel the material break.
Step 8. Every few turns, remove the tap (by turning counterclockwise) to remove the shavings
This is especially important for blind holes, those that do not go through the full thickness of the workpiece.
Step 9. When the tap has reached the desired depth, pull it out, clean the chips and any cutting fluids or lubricants, and test your screw or bolt in the new thread
Advice
- Small males break apart very easily. It only takes 2 kg of force to break a male for M3, so be very careful when using them.
- Tapping produces chips. Cover any part of the piece to be threaded or surrounding areas that could be damaged by shavings, or clean up when finished.
- Larger taps, such as the one for M18, remove too much material to be used manually, unless they are particularly strong.
- In case of very thin objects to be threaded, it is advisable to use a nut on the other side. Alternatively, specific rivets can be used for metal sheets and threaded inserts for softer materials, such as plastic. For metals it is a good rule that there are at least three complete threads.
- The tool used to carve the male threads of the screws is called a die.
- Make sure you don't change the pitch angle of the tap, especially at the beginning. Making a single thread is better than making two or more.
- With ductile materials, taps are often used that are capable of threading by plastic bearing of the material, not by carving.
Warnings
- For threads that have to withstand loads, you should always check that the threads, fasteners and materials are suitable.
- The taps are made of hardened steel, which guarantees long life and sharp surfaces; however this makes it fragile. Taps are expensive and the piece to be threaded could be much more. Always use lubricants and be very careful when tapping.
- On very resistant materials such as certain types of stainless steel you have to choose between a very difficult machining or a tolerance class of the thread coupling less than the usual 6h, making a slightly larger hole for tapping.
